Notes on xargs syntax for parallel execution

xargs_parallel_syntax.sh

#!/bin/bash
## space-separated input
## -n1: run each separately
## -P6: run up to 6 in parallel
## -I '{}': replace {} with argument
## \$ delays evaluation to bash execution
## waits randomly for up to five seconds, then prints
echo {1..12} |\
  xargs -n1 -P6 -I '{}' \
  bash -c "sleep \$[ \$RANDOM % 5 ]; echo {}"